Heart Disease in Dogs

Heart Disease in Dogs

The canine heart is a hard-working organ, and is divided anatomically into left and right sides; valves allow for blood flow through the heart. The left atrium, the right atrium, the left ventricle, and the right ventricle comprise the four heart chambers. The external heart “sac” is designated the pericardium, and the myocardium is the actual muscle of the heart. The endocardium is the inner layer of cells in the heart. Heart disease, or cardiac disease, can affect any of these components.

“Dirty” blood (carrying carbon dioxide from organs, tissues, and cells) enters the right atrium through large vena cavae veins and flows to the right ventricle via the tricuspid valve. It travels through the pulmonary artery (via the pulmonary valve) to the lungs to collect oxygen and eliminate carbon dioxide and re-enters the left atrium through the pulmonary vein. The mitral valve ferries the oxygen-rich blood to the left ventricle, and the aorta (entering through the aortic valve) carries “clean” oxygen-rich blood to the remainder of the body.

Heart disease, or cardiac disease, can be a devastating clinical condition in companion animals. Early recognition and treatment can facilitate appropriate clinical management and a long life.

Types of Heart Disease in Dogs

Cardiac disease is classified as either congenital or acquired.

Most congenital cardiac defects are present from birth or near birth, and include conditions such as septal defects (atrial and ventricular), valve dysplasias, patent ductus arteriosus tetralogy of fallot, vascular ring anomalies, aortic, pulmonic, and mitral stenosis, and cor triatriatum dexter. All involve some degree of structural heart component or valvular dysfunction.

Although some breed-associated congenital conditions are detected early in life, others are not identified until adulthood. Cavalier King Charles spaniels, Doberman Pinschers, Boxers, and Newfoundlands are among breeds frequently diagnosed with familial cardiac conditions.

Acquired conditions can also affect any heart component and are not present at or near birth. They develop over time and with age and many are not pathologic or progessive. However, some may be associated with progressive heart and valve disease.

Endocarditis, myocarditis, and pericarditis are structural inflammatory conditions that result from a variety of causes, including infectious, traumatic, and immune conditions.

Pericardial effusion occurs when excessive fluid collects between the layers of the pericardial sac; causes are diverse and can include cancer.

What is a Heart Murmur

A heart murmur is an extra sound detected by the veterinarian during the physical examination; such murmurs usually develop secondary to turbulent blood flow. Heart murmurs are identified in patients with and without heart disease.

Many murmurs are innocent, particularly those identified in young puppies, without any evidence of cardiac disease. They are soft murmurs and usually disappear on their own. Other benign murmurs are seen secondary to anemia (decreased red blood cell count), pain, and intense excitement.

Pathologic murmurs may have very characteristic sounds and locations and are associated with cardiac disease.

Clinical Signs and Complications of Heart Disease in Dogs

Clinical signs in dogs include:

Pale or lilac-colored mucous membranes

Weak pulses

Cold extremities

Poor circulation

Fainting

Jugular vein pulses

Breathing difficulties

Coughing

Exercise intolerance

Heart murmurs

Clots in the arteries

Fluid collection in the abdomen

Edema or swelling of the limbs

Weight loss (cardiac cachexia)

Breathing difficulties are an extremely common cardiac complication in dogs because of fluid retention inside or outside the lungs.